1. Technical Field
The present invention relates to coil units, and power transmission devices and power reception devices using the coil units.
2. Related Art
In recent years, contactless power transmission (non-contact power transmission) that utilizes electromagnetic induction to enable power transmission without metal-to-metal contact has been attracting attention. As application examples of non-contact power transmission, charging a portable telephone, charging a household appliance (e.g., cordless telephone handset), and the like have been proposed.
JP-A-2005-006396 (Patent Document 1) is an example of related art of the contactless power transmission. According to Patent Document 1, a power transmission device and a primary coil to which an output of the power transmission device is applied are provided on a charging side, and a secondary coil to be electromagnetically coupled to the primary coil, a power reception device that generates a DC voltage from an output of the secondary coil, and a secondary battery that is charged based on the output of the power reception device are provided on a power receiving side. Patent Document 1 further describes a charge control device (8) that monitors the state of charging progression and varies the AC frequency of the power transmission device to a specified value according to the state of charging progression. For performing the charging control, a coil pair (an auxiliary transformer 85) for communication is independently provided in addition to the primary and secondary coils for power transmission.
JP-A-11-332135 (Patent Document 2) is another example of related art that describes a secondary coil (210) that is commonly used for power transmission and communication. According to Patent Document 2, a secondary coil (210) is provided on an electronic clock (200) on the power receiving side, and an inner peripheral coil (110a) and an outer peripheral coil (110b) arranged in a concentric manner at positions opposite to the secondary coil (210) are provided in a station (100) on the power receiving side. When transmitting power to the electronic clock (200) at the station (100), the outer peripheral coil (110b) with a fewer number of turns is used. On the other hand, when transmitting signals to the electronic clock (200), a serial coil composed of the inner peripheral coil (110a) and the outer peripheral coil (110b) is used.
According to Patent Document 1, the coil pair for communication must be provided independently, in addition to the primary coil and the secondary coil for power transmission. According to Patent Document 2, the inner peripheral coil (110a) and the outer peripheral coil (110b) arranged in a concentric manner need to be provided as the primary side coil.